The invention relates to an assembly of a running rail and a running gear for the drive mechanism for a rail-guided displacement device, such as a stair lift. Such assembly is known from GB 2 168 019.
This known assembly comprises a running gear having a main frame and a pair of pivotable subframes, each of the subframes provided with guide wheels running on either side of the running rail. The subframes are each pivotable around an axis parallel to the axes of the guide wheels, extending perpendicular to the length of the running rails in the middle between said axis of said guide wheels. The facing sides of the subframes are provided with a curved surface having teeth, said teeth of said subframes meshing and providing for a mechanical mirror. Between the pairs of guide wheels on both subframes two further guide wheels are provided, positioned on both sides of the running rail. One of these further guide wheels is coupled to a pivotable rod which, through teeth and cooperating teeth on one of the subframes provides for pivoting of said subframe when running through a curve in a plane perpendicular to the axis of the guide wheels, which pivoting provides for the mirrored pivoting of the other subframe by means of the meshing teeth. Furthermore, a drive wheel is provided for movement of the running gear along said guide rails. The rotation axis of the drive wheel lies within the mirror plane between said subframes.
In this known running gear the chair is coupled to two flanges extending on either side of the running gear, in which bearings are provided for the pivoting axis of both subframes, as well as the axes of the pivoting member providing for the mirrored movements of said subframes. Therefore the chair follows the movements of the rotation axes of said subframes, which means that there will be movement of the chair relative to the drive wheel.
In using an assembly of this known type load carrying means will move in a direction perpendicular to the running rail, relative to the drive wheel when negotiating curves. Therefore, when the drive wheel is driven with a constant speed the chair is accelerated and decelerated when negotiating said curve, since the path of travel of the chair is either longer or shorter than the relative part of the guide track, depending on whether the curve is facing downward or upward. These accelerations and decelerations should be avoided for comfort of a passenger or other load and in order to keep the forces exerted on the running gear as low as possible.
This known assembly furthermore involves the drawback that when traversing a curve, the guide wheels will assume an undesired position relative to the running rail, because the position of the guide wheels relative to the rigid supporting part, made up of at least the two flanges and the axis of the guide wheels remains the same. In particular for guide wheels that do not lie in or parallel to the plane of the curve, this means that additional wear of the different parts such as wheel bearings and wheel tread occurs, because the axis of rotation of the relevant guide wheel is not at right angles to the tangent to the curve part in which the guide wheel is located. In other words, when traversing the curve, the tread of the wheel in question is always slightly oblique relative to the instantaneous line of movement to be travelled thereby. This applies to driven as well as to non-driven running gears of the known type.
A further assembly of the above-mentioned type is known from practice and is supplied by the firm of Thyssen de Reus, Krimpen aan de IJssel, the Netherlands.
The known running gear consists of a profiled guide rail along which a displacement device in the form of a lift for with the invention, a running gear is characterized in that the swivel axle of each frame part is spaced from a rotary shaft plane of said each frame part, said rotary shaft plane defined by at least two rotary shafts of respectively the set of guide wheels associated with each said frame part, the bridge piece including the third set of guide wheels which lie approximately in the plane of symmetry (S) and which, during use, have a supporting function, and the bridge piece having fastening means for a load to be carried drive wheel included in the running gear and a gear rack provided on the running rail. To ensure that the drive wheel remains in contact with the gear rack, a set of guide wheels is provided on both sides of the rail and on both sides of the drive wheel. The guide wheels are rotatable about shafts that fixedly connected to a supporting part, which supporting part moreover carries the drive wheel and a drive motor, if any.
The rigid supporting part of this known running gear has the advantage that thus a proper contact between the gear rack and the drive wheel is obtained and maintained, at least in the case of a relatively straight or only slightly bent running rail. When sharper curves are traversed, such a device has the drawback that the guide wheels should have a play such that they can move along both on the outside and on the inside of the curve without the drive wheel either moving away too far from the running rail, if the drive wheel is located on the inside of the curve in the running rail, or being pressed too tightly against the running rail or the gear rack, if the drive wheel is located on the outside of the curve. In the first case, the contact between the drive wheel and the gear rack will get lost, in the second case the drive wheel may seize and/or damage may be caused to the drive wheel and the gear rack. This problem can slightly be overcome by shortening the distance between the guide wheels on both sides of the drive wheel, but this affects the stability of the running gear adversely, which is undesirable, in particular in the case of, for instance, passenger lifts, which require that the user's safety be guaranteed at all times.
It has already been proposed to position the guide wheels on both sides of the running rail further apart than the width of the intermediate running rail. Although this enables a curve to be traversed more properly, it will also involve instability of the running gear, and, accordingly, of the stair lift, because at least in a straight running rail portion, the guide wheels then no longer abut against the running rail. Hence, for safety reasons, such an embodiment is less suitable.